This is the correct answer and is much more consistent than any of the other options, resulting in much greater precision when tracking time. One second is defined to be 9 192 631 770 vibrations of a Cesium atom.
Which of the following would serve as the best time standard?
a. the buzzing of a mosquito
b. the rotation of Earth upon its axis
c. the vibration of a CS-133 atom
d. a grandfather clock